1. Field of the Invention
The subject invention relates to light gate utilization methods and apparatus, and extends in its utility to methods and apparatus for recording varying electrical signals and methods and apparatus for reading information with the aid of light gates. Examples of such apparatus include solid state oscillographs and solid state facsimile equipment.
The subject invention also relates to increased-density electrode arrays, to optical systems for converting a spatially concentrated light output into a band of light, and to electro-optical systems for modulating a light output.
2. Description of the Prior Art
A family of ferroelectric electro-optic ceramics is known as PZT compounds with P standing for lead, z for zirconium and T for titanium. Under the influence of an electrical field, PZT compounds become birefringent and exhibit various electro-optic properties. For instance, incoming light is resolved into two component waves propagating at different velocities and in polarization planes that are at right angles to each other. The magnitude of the effect is a function of the applied voltage and of the light frequency. Light valves and gates may be provided by placing the electro-optic ceramic between a polarizer plate and an analyzer plate.
A breakthrough occurred with the discovery that substitution of small amounts of lanthanum greatly improves ferroelectric properties. These improved compounds generally have become known as PLZT compounds, with the L standing for lanthanum.
Reference may in this respect be had to Land et al, Ferroelectric Ceramic Electrooptic Materials and Devices, 57 Proceedings IEEE No. 5, May 1969, pp. 751 to 768, Thacher et al, Ferroelectric Electrooptic Ceramics with Reduced Scattering, ED-16, IEEE Transactions on Electron Devices, No. 6, June 1969, pp. 515 to 521, Maldonado et al, Ferroelectric Ceramic Light Gates Operated in a Voltage-Controlled Mode, ED-17, IEEE Transactions on Electron Devices, No. 2, February 1970, pp. 148 to 157, New Ferroelectric Ceramics Enhance Electro-Optic Performance, Design News, June 22, 1970, pp. 10 and 11, Haertling et al, Hot-Pressed (Pb, La) (Zr, Ti) O.sub.3 Ferroelectric Ceramics for Electrooptic Applications, 54 Journal of The American Ceramic Society, No. 1, January 1971, pp. 1 to 11, Waterworth et al, Integrated Electro-Optic Modulator Arrays, 4 Opto-electronics (1972) 339 and 340, Cutchen et al, Electro-optic Devices Utilizing Quadratic PLZT Ceramic Elements, 30, 1973 Wescon Technical Papers, Vol. 17 pp. 1 to 12, Zook, Light Beam Deflector Performance: a Comparative Analysis, 13 APPLIED OPTICS, No. 4, April 1974, pp. 875 et seq., Fiber Display Features Digital Scanning, Optical Spectra, June 1974, and Cutchen et al, PLZT Electrooptic Shutters: Applications, 14 APPLIED OPTICS, No. 8, August 1975, pp. 1866 to 1873.
In the course of such development, replacement of Kerr cells in such applications as constant-density trace oscillographs disclosed in U.S. Pat. No. 3,354,465 by Merritt et al, issued Nov. 21, 1967, were replaced by solid-state light valves. Indeed, solid-state shutter systems were among the first practical applications as may, for instance, be seen from U.S. Pat. No. 3,555,987, by Iben Browning, issued Jan. 19, 1971. The switching properties and modes of ferroelectric ceramic plates were recognized and published such as in the above mentioned 1969 IEEE article by Land et al, pp. 61 and 762 and FIG. 20, and proposals for practical applications such as those suggested in the above mentioned U.S. Pat. No. 3,930,119, by Schmidt et al, issued Dec. 30, 1975, naturally followed.
Similarly, PLZT electro-optic modulator arrays of the type disclosed in the above mentioned 1972 Opto-electronics letter by Waterworth et al have been considered suitable as the light modulating agency in a solid state oscillograph. In a similar vein, a PLZT device has been considered as an electrooptic shutter in an oscillograph of the Type 5-134 and the Type 5-139 manufactured by the subject assignee.
These installations, of course, still operated with conventional galvanometer mirrors, leaving unsatisfied the need for a solid state recording oscillograph using a PLZT or other type of solid state light gate structure. However, the prior art was notoriously unable to overcome various obstacles, entrenched prejudices and inadequacies which remained in the way of competitive solid state oscillograph and facsimile writing and reading equipment.
This will presently be explained with the aid of the above mentioned U.S. Pat. No. 3,930,119, by Schmidt et al, issued Dec. 30, 1975. It is to be pointed out in this connection that the problems presently to be discussed are endemic to the prior art and that the Schmidt patent has been selected as a convenient basis for discussion because of its symptomatic nature and relatively recent date.
One of the prevailing problems becomes apparent from a consideration of the fact that an effective light gating action requires each electrode or at least one electrode of each electrode pair to be individually connected to its own electric energizing wire. In this respect, several electrodes per millimeter have to be provided for adequate resolution. By way of example, Schmidt et al mention an array of 1,200 lines of 800 picture elements each. At such high densities, the requisite individual terminal for each electrode becomes larger than the electrode itself, as may be seen from FIG. 12 on page 1871 of the above mentioned Cutchen article entitled PLZT Electrooptic Shutters: Applications. Accordingly, the inevitable minimum terminal size in practice is the limiting factor of electrode density and scanning or picture element resolution.
Another problem stems from the high light indensity required for solid state light gate operations. While arc lamps and other high-indensity or point-type light sources exist, the problem becomes acute when an elongate light gate array is to be illuminated for selective light transmission. In this respect, the above mentioned Schmidt et al patent proposes use of a tubular light source coextensive with the longest dimension of the light gate array and providing a uniform illumination there across. No existing light source having such elongate, coextensive configuration and meeting the applicable collimation requirements could be found.
In a similar vein, the well-known light scattering properties of PLZT and other solid state light gates, coupled with the natural difraction imposed on light coming through a multitude of narrow light gates, impose strict requirements, including collimation in two crossed directions to avoid sideways spread of the recording or illuminated reading point and to facilitate focusing of gated light to a small spot in the direction of travel of the recording medium or the master to be read.
Such bidirectional collimation appears lacking from the Schmidt et al proposal. No remedy for this defect could be found in the remainder of the above mentioned references.